Angelina Jolie revealed on Monday that she underwent a preventative double mastectomy after discovering that she carries the BRCA1 gene that increases her risk of developing breast cancer. The Oscar winner wrote about her decision in a riveting op-ed piece in the New York Times, “My Medical Choice.” Angelina Jolie's medical decision has sparked many reactions from celebrities on Twitter, including some from stars who've been faced with similar decisions. For the latest entertainment news tune into “omg! Insider” on TV tonight.